1. Field of the Invention
This invention relates to a cleaning device, and, more particularly, it is concerned with a cleaning device which removes the magnetic developer remaining on the surface of an image bearing member after the magnetic developer image formed on the image bearing member has been transferred onto a recording medium.
2. Description of the Prior Art
There have already been known various types of cleaning devices for removing residual toner from the surface of a latent image bearing member such as a photosensitive member, etc. which is a medium for visualizing an electrostatic latent image: for example, a "web cleaning" device, in which the toner is wiped off by means of a member like unwoven cloth (vide: e.g. U.S. Pat. No. 3,099,856 to R. H. Eicoru et al.), and a "blade cleaning" device, in which the toner is scraped off by a blade member (vide: e.g. U.S. Pat. No. 3,552,850 to S. F. Royka et al.). The former was adopted at the early stage of development of electrophotographic apparatus. This device wipes off the residual toner and simultaneously adheres the same onto a web. While it has an advantage of less scattering of the toner particles, it has disadvantages in that the device becomes complicated in construction and large in size. In comparison with the former, the latter attempted to reduce the size and weight of the device as well as improve its maintenance capability, although it still has the disadvantage of prohibitive toner scattering in comparison with the former device, wherein the toner is perfectly adsorbed onto the web. A possible reason for this is considered as follows: (1) the toner which has been scraped off by a blade freely drops into the recovery section and scatters due to shock at the time of its dropping; (2) the cleaning blade made of a resilient material brings about the so-called "stick-slip" vibrations to cause the toner to scatter during its removal. Explaining this latter point in more detail, the cleaning blade is made of an elastic material such as, for example, urethane rubber, etc. in order to prevent its adherence to the irregular surface of the image carrying member as well as to prevent damage caused to the surface of the image carrying member. Because it is made of such elastic material, however, the blade is subjected to compression-deformation due to frictional force with the image carrying member. This compression force in the blade gradually increases, and a greater compression force than the frictional force is transitionally accumulated in it. The thus augmented compression force will soon be sufficient to counter the frictional force, and be dissipated, whereby the cleaning blade instantaneously stretches over the surface of the image carrying member. This behavior occurs periodically causing the cleaning blade to vibrate and the toner to scatter. Since it is difficult to perfectly eliminate the causes for the toner scattering, various attempts have been made to provide a construction to prevent the toner from scattering. For example, a system of preventing the toner scattering has been proposed, as disclosed in U.S. Pat. No. 3,634,077, wherein a developing agent removed by the cleaning blade is adsorbed onto a roller surface, to which a voltage has been applied from a power source. In this system, while effective adsorption of the scattering developer can be attained, it becomes inevitably necessary to provide the voltage source to apply voltage to the adsorbing roller, with the consequence that the cleaning device as a whole tends to be large in size.
Further, there has been proposed another system, as taught in U.S. Pat. No. 3,742,551, wherein an elastic roller is provided beneath the cleaning blade, and, while causing it to contact lightly onto the surface of the photosensitive drum to follow its rotation, the dropping and scattering of the toner is prevented. While this system can also attain the effect of preventing scattering of the removed developing agent, it has the disadvantage that, owing to direct contact of the elastic roller surface to the photosensitive drum surface, the surface of a latter is stained, as the result the image forming effect is appreciably lowered in the course of its use over a long period of time.
Incidentally, the developing agent to be used for the electrophotographic reproduction apparatus has recently been changed from the two-component system toner consisting of a toner and a carrier to a single-component toner (magnetic developing agent) consisting of a magnetic material as a nucleus and a coloring substance covering the outer surface of the nucleus. The characteristic feature of this single-component toner resides in that the density of the developer is constant, hence there is no necessity for density adjustment. As a result of this, the electrophotographic reproduction apparatus can be made simple in construction. However, even when this single component system toner is used, the toner scattering would inevitably occur at the time of removing the residual toner, as already mentioned in the foregoing.
Furthermore, the electrophotographic reproduction apparatuses which have been manufactured recently are required to be of a resources-saving and non-polluting type. In order to meet such requirement, the apparatuses should be of such a design that, for example, (1) the removed toner may be transferred to the developing device for re-use, and (2) the toner is collected into a toner recovery box, which will then be discarded.